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Si1−xGex alloy films and SimGen superlattices (SLs) were prepared by molecular beam epitaxy on 〈001〉 silicon wafers. The crystalline quality of the films is characterized by analyzing the x-ray diffraction pattern. The intensity measured at constant diffraction angle provide (by rocking the sample) the distribution of the angles made by the diffraction planes in the film with the substrate. The lattice constants indicate the strain conditions in the films. A relationship between the strain and the width of the diffraction peaks is shown. Si1−xGex alloy films on 〈001〉 Si are used as a buffer layer, i.e., as a virtual substrate for SimGen SL. The SimGen SL parameters are obtained from the satellite position around the (004) Bragg reflection. Fitting the satellite intensities yields the average lattice parameter of the single Si and Ge layers. A comparison of different SLs reveals a significant dependence of the lattice parameters on the thickness of the Si1−xGex alloy buffer layers.

Photoconductivity (PC) spectroscopy is used to determine the optical absorption and behavior of free carriers of Si/Ge structures and (Si6Ge4)100 superlattices grown on Si0.4Ge0.6 alloys. Negative photoconductivity is observed at a temperature of 67 K. Some samples are additionally doped by nuclear transmutation. These samples exhibit a strong negative PC signal even at room temperature, which cannot be suppressed by a bias illumination.

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